a. Field of the Invention
The present invention relates to a heat sensitive recording material which comprises a support having thereon a heat sensitive layer and, more particularly, to a heat sensitive recording material which has a heat sensitive layer excellent in transparency.
b. Description of the Prior Art
A heat sensitive recording method has many advantages in that, (1) no particular developing step is required, (2) if paper is used as a support, a recording material prepared can have a quality akin to that of plain paper, (3) handling of a recording material used is easy, (4) images recorded has high color density, (5) this method can be embodied using a simple and cheap apparatus, (6) no noise is generated upon recording, and so on. Therefore, heat sensitive recording materials have recently enjoyed a markedly increasing demand, particularly in the fields of facsimile and printer, and have come to be used for many purposes.
With this background, it has come to be desired to develop transparent heat sensitive recording materials which enables direct recording with a thermal head in order to adapt them for multicolor development, or to make them usable for an overhead projector (hereafter it is written as OHP).
However, conventional transparent heat sensitive recording materials are so-called transparent heat sensitive films in which the film is brought into direct contact with an original and exposed to light, and thereby an infrared portion of the light is absorbed by image areas of the original to raise the temperature of the image areas, which results in color development of the heat sensitive film. Accordingly, they do not have heat sensitivity high enough to enable direct heat recording with a thermal head to be used in facsimile and the like.
In addition, a heat sensitive layer of heat sensitive recording materials of the kind which use a thermal head upon heat recording is in a devitrified condition, so a desired transparency cannot be achieved by merely coating such a layer on a transparent support.
As the result of concentrating our energies on study of heat sensitive recording materials, it has now been found that when a combination of a colorless or light colored precursor of a basic dye and a color developer is employed as color development system, the former is microencapsulated and the latter is emulsified and dispersed under a prescribed condition, and then both are mixed and coated on a support, the heat sensitive layer formed becomes transparent to our surprise, thus achieving the present invention.